The present disclosure relates to a solid-state imaging device, its manufacturing method and electronic apparatus each making use of the solid-state imaging device.
An electronic apparatus such as a digital camera employs a solid-state imaging device. For example, an electronic apparatus employs a CMOS (Complementary Metal Oxide Semiconductor) image sensor serving as the solid-state imaging device.
The solid-state imaging device includes a plurality of pixels laid out in a pixel area of a semiconductor substrate. Each of the pixels has an opto-electrical conversion section. A typical example of the opto-electrical conversion section is a photodiode in which incident light is received by a light receiving surface and subjected to an opto-electrical conversion process in order to convert the light into signal electric charge.
In a CMOS image sensor, which is a typical solid-state imaging device, each pixel is configured to include a pixel transistor circuit in addition to an opto-electrical conversion section. The pixel transistor circuit is configured to read out signal electric charge generated by the opto-electrical conversion section, and output the signal electric charge to a signal line as an electrical signal.
In a solid-state imaging device including a plurality of opto-electrical conversion sections laid out on a semiconductor substrate, in general, a multi-layer wiring layer is provided on the front-surface side of the semiconductor substrate and incident light coming from the front-surface side is received by the light receiving surface of the opto-electrical conversion section. A solid-state imaging device having such a configuration is referred to as a solid-state imaging device of the front-surface radiation type. Thus, in the case of the front-surface radiation type, the multi-layer wiring layer having a large thickness exists at a position between a micro-lens and the light receiving surface. In consequence, wires reduce the aperture ratio. As a result, it may be difficult to improve the sensitivity in some cases.
In order to solve the problem described above, there has been proposed a configuration in which incident light comes from the rear-surface side of the semiconductor substrate is received by the opto-electrical conversion section. The rear-surface side of the semiconductor substrate is a side opposite to the aforementioned front-surface side on which the multi-layer wiring layer is provided. A solid-state imaging device having such a configuration is referred to as a solid-state imaging device of the rear-surface radiation type. For more information on the rear-surface radiation type, the reader is advised to refer to documents such as Japanese Patent Laid-Open Nos. 2010-109295, 2010-186818 and 2007-258684.
In the case of the rear-surface radiation type, the thickness of the semiconductor substrate is reduced to a value of the order of 3 μm. In consequence, incident light passing through the semiconductor substrate may be reflected by the wires included in the multi-layer wiring layer and may propagate back to the photodiodes laid out on the semiconductor substrate in some cases. Thus, in such cases, a signal generated by a photodiode includes noises which reduce the quality of the taken image.